Ion-beam irradiation of Gd₂Sn₂O₇ and Gd₂Hf₂O₇ pyrochlore: Bond-type effect

Ceramics with III-IV pyrochlore compositions, A³⁺₂B⁴⁺₂O₇ (A = Y and rare earth elements; B = Ti, Zr, Sn, or Hf), show a wide range of responses to ion-beam irradiation. To evaluate the role of the B-site cations on the radiation stability ofthe pyrochlore structure-type, Gd₂Sn₂O₇ and Gd₂Hf₂O₇ have been irradiated by1 MeV Kr⁺. The results are discussed in terms of the ionic size and type ofbonding of Sn⁴⁺ and Hf⁴⁺ and compared to previous results for titanate andzirconate pyrochlores. Gd₂Sn₂O₇ is sensitive to ion beam–induced amorphizationwith a critical amorphization dose of approximately 3.4 displacements per atom(dpa) (2.62 × 10¹⁵ ions/cm²) at room temperature and a critical amorphization temperature of approximately 350 K. Gd₂Hf₂O₇ does not become amorphous at adose of approximately 4.54 displacement per [lattice] atom (3.13 × 10¹⁵ ions/cm²) at room temperature, but instead is transformed to a disordered fluorite structure upon ion-beam irradiation. Although the radius ratio of the A- to B-site cations provides a general indication of the type of radiation response of different pyrochlore compositions, the results for Gd₂Sn₂O₇ emphasize the importance of bond type, particularly the covalency of the 〈Sn–O〉 bond in determining the radiation response.